In the struggle to slow the runaway freight train of humanity's destructive impact on Earth, scientists are increasingly looking at the role our oceans can play.
Teaming up with industry, scientists from the University of Southern California have discovered a 'kelp elevator' technique that produces ample seaweed, potentially providing a high-yield biofuel to help wean us off fossil fuels.
Many land-based biofuels capable of powering cars, planes, ships, and trucks are currently sourced from mass-produced farm crops like corn, soybeans, and switchgrass. There are several problems with these options, including using up limited food-providing land space, guzzling massive amounts of water, pollution from pesticides and fertilizers, and encroaching on rare biodiverse habitats.
Not only does relying on giant marine algae like seaweed avoid these problems, but the biology of seaweed is also more suited to use as a biofuel.
Giant kelp (Macrocystis pyrifera) can grow at an impressive rate of up to 35 cm (14 inches) a day, in ideal conditions. They constantly form new fronds, allowing the harvesting of the mature fronds, which can reach 30 metres (98 feet) in length and would otherwise just deteriorate and die, without impacting the kelp's growth.
As kelp is a protist, rather than a plant, its molecular composition lacks the sturdy plant lignin that complicates the process of converting land crops into fuel. Furthermore, growing kelp also captures carbon dioxide, which in turn elevates pH levels and oxygen supplies in the immediate areas – helping mitigate the local effects of ocean acidification.
But questions remain over whether we can farm enough seaweed to fuel our future in an environmentally friendly way. Now, researchers may have discovered a way to effectively mass produce kelp - by raising and lowering kelp's depth in the water.
"We found that depth-cycled kelp grew much faster than the control group of kelp, producing four times the biomass production," University of Southern California environmental scientist Diane Young Kim said.
By cycling the depth of the kelp across a day, the team discovered it was taking nutrients from deeper in the water that were missing closer to the surface at night, fueling its extra growth, while still receiving enough access to sunlight in shallower depths during the day.
The team found the kelp exposed to greater depths experienced some physiological changes that made them better equipped to deal with the increased pressure. Their pneumatocysts – the air-filled structures that help kelp fronds float closer to the sun – became thicker and more filled with fluid.
The researchers built a kelp elevator off the coast of California out of fibreglass and stainless steel, with horizontal beams they could "plant" juvenile kelp on. The whole structure was cycled through the water column using an automated, solar-powered winch.
"The good news is the farm system can be assembled from off-the-shelf products without new technology," explained one of the team, chief engineer of Marine BioEnergy Brian Wilcox. "Once implemented, depth-cycling farms could lead to a new way to produce affordable, carbon-neutral fuel year-round."
This technique could open up to farming huge regions of nutrient-poor ocean where kelp wouldn't usually grow, which would allow us to also protect vital carbon sinks of naturally occurring kelp forests while still making use of the brown algae.
The team urged further investigation in this area as much remains to work out before we can see if this idea really is as good as it sounds, including the costs and energy requirements involved in growing, transportation, and converting the kelp biomass into liquid fuels.
But other scientists, like Woods Hole Oceanographic Institution biologist Scott Lindell, are also working on selectively breeding hardier and larger kelp species that would be even more suitable for use as a biofuel.
"In a hotter and drier world of the future," Lindell said in 2019, "it will be hard to find a better resource for biofuels than farmed seaweeds that require no arable land, no fresh water, and no fossil-fuel-derived fertilizer in contrast to modern land crops."
This research was published in Renewable and Sustainable Energy Reviews.